a parable combined with a riddle, most commonly associated with the teaching of Zen buddhism. A koan confronts the student with a seemingly impenetrable question which is only resolved when through acheiving a deeper understanding of the philosophical point being taught.
One of the most famous koans is "What is the sound of one hand clapping?"
Someone who invents sexual conquest stories to sound superior or to impress friends.
Guy 1: Dude that guy is such a Koan.
Guy 2: Yeh man I know last week he told me he lost his virginity giving a girl a dirty sanchez when he was 14.
Guy 1: Haha. What a loser.